[MIM 614 490]

A very rare blood group, mainly found in patients of Japanese origin, Bedouins and the Roma population. This system is defined by the presence or absence of the Jr(a) antigen. The majority of the population carries this antigen. Autosomal recessive transmission of a mutation of the ABCG2 gene (4q22.1), coding for the ATP-binding cassette transporter ABCG2, which transports uric acid and carries the Jr(a) gene.

Patients lacking this antigen on the surface of red blood cells develop anti-Jr(a) antibodies, which can lead to hemolytic disease of the newborn or a delayed transfusion reaction in the presence of Jr(a)-positive blood.

The term JR comes from the initials of one of the first patients in whom it was described: Jacobs Rose. The term junior derived from it is in fact an error.

Anesthetic implications:

use of Jr(a)-blood in these patients

References : 

-          Castilho L, Reid ME.
A review of the JR blood group system.
Immunohematology 2013;29 :63-8

Updated: March 2025